Metabolic and bariatric surgery

Metabolic and bariatric surgery is a category of surgical procedures used to treat obesity and weight-related health conditions. Indications include BMI ≥ 35 kg/m² and BMI 30–34.9 kg/m² with an uncontrolled weight-related health condition. The most common procedures are sleeve gastrectomy and Roux-en-Y gastric bypass. Preoperative assessment includes clinical evaluation, laboratory studies, lifestyle assessment, and a formal psychosocial-behavioral health evaluation. Preoperative and postoperative management involves lifestyle modification and medication adjustment. Long-term follow-up is needed to monitor weight loss, provide micronutrient supplementation, evaluate for complications, and manage comorbidities. Early complications include bleeding, anastomotic leak, and bowel obstruction. Common late complications include abdominal pain, malabsorption, dumping syndrome, and gastroesophageal reflux disease (GERD). Complications specific to gastric bypass (e.g., Roux-en-Y) include small intestinal bacterial overgrowth and marginal ulcers.

Adults ^[1]

• Body mass index (BMI) ≥ 35 kg/m² (class 2 obesity or class 3 obesity)
• BMI 30–34.9 kg/m² (class 1 obesity) with both:
  • Type 2 diabetes mellitus and/or another weight-related health condition
  • AND lack of significant weight loss and/or improvement in that condition following nonsurgical interventions
• BMI ≥ 27.5 kg/m² in individuals of Asian descent

Children ^[2]

Metabolic and bariatric surgery is typically only recommended for individuals aged ≥ 10 years.

• BMI ≥ 140% of the 95th percentile (class 3 obesity) OR BMI ≥ 40 kg/m²
• BMI ≥ 120% of the 95th percentile (class 2 obesity) OR BMI ≥ 35 kg/m² with a significant weight-related health condition, e.g.:
  • Type 2 diabetes mellitus or insulin resistance
  • Hypertension
  • Hyperlipidemia
  • Orthopedic disease (e.g., Blount disease, SCFE)

Refer all patients ≥ 13 years of age with class 2 obesity and higher to a surgical center for evaluation. ^[3]

Absolute ^[4][5]

• Inability to understand the procedure and/or follow the management protocol
• Reversible medical cause of obesity (e.g., hypothyroidism) ^[6]
• Limited life expectancy
• Current pregnancy or pregnancy planned within the next 12–18 months
• Allergy to general anesthesia
• Comorbidities
  • Decompensated cirrhosis
  • Uncorrectable bleeding disorder
  • Uncontrolled peptic ulcer disease
  • Current psychosis and/or recent hospital admission for psychosis
  • Current suicidal ideation and/or recent suicide attempt

Relative ^[4][5]

• Significant cognitive impairment
• Older adults with frailty ^[1]
• Age < 10 years ^[2]
• Individuals who are nonambulatory
• Comorbidities
  • Severe lung disease
  • Unstable coronary artery disease
  • Severe heart failure
  • Active cancer (or ongoing cancer treatment)
  • Substance use disorder (alcohol, drugs)
  • Crohn disease (for Roux-en-Y gastric bypass)
• Current tobacco use ^[5]

We list the most important contraindications. The selection is not exhaustive.

Preoperative evaluation ^[5]

The preoperative evaluation involves a complete history, mental health evaluation, physical examination, and diagnostic studies to assess operative risk.

Clinical evaluation

• Measure weight and BMI.
• Evaluate for:
  • Causes of obesity
  • Weight-related health conditions
  • Contraindications to metabolic and bariatric surgery
• Ask about:
  • Previous weight-loss strategies and outcomes
  • Lifestyle (e.g., diet, exercise, sleep, mood, substance use, community involvement)
• Assess motivation to follow postoperative management protocol.
• Refer for nutritional evaluation by a dietitian.
• Refer for formal psychosocial-behavioral health evaluation, and assess need for individual psychological counseling or management.
• See also "Preoperative clinical evaluation."

Diagnostic studies

• All patients
  • Routine blood tests: CBC, CMP, fasting blood glucose, fasting lipid panel, prothrombin time, blood typing
  • Nutritional screen: iron studies, vitamin B₁₂, folate, vitamin D, vitamin B₁, vitamin A, vitamin E, vitamin K, zinc, copper
  • Urinalysis
  • Ensure cancer screening is up to date.
• Select patients
  • Endocrine studies based on clinical suspicion
    • Hemoglobin A1C
    • TSH
    • Diagnostics for polycystic ovarian syndrome (e.g., testosterone, androstenedione, and dehydroepiandrosterone)
    • Diagnostics for Cushing syndrome (e.g., low-dose dexamethasone suppression test)
  • Polysomnography if screening for obstructive sleep apnea is positive
  • ECG if clinically indicated (e.g., ASCVD risk factors)
  • Echocardiography if clinically indicated (e.g., pulmonary hypertension and/or a cardiac condition is suspected)
  • EGD if clinically indicated (e.g., clinical features of GERD) ^[5]
  • Ultrasound abdomen if clinically indicated (e.g., clinical features of gallstones, elevated liver chemistries)
  • Helicobacter pylori diagnostics if in a high-prevalence area

Refer patients with known heart disease or intrinsic lung disease for formal evaluation by a cardiologist or pulmonologist, respectively. ^[5]

Preoperative management ^[5]

• Patient education
  • Counsel on preoperative lifestyle modifications, including tobacco cessation > 6 weeks (ideally 1 year) before surgery. ^[5]
  • Advise pregnancy prevention until 12–18 months after surgery in patients who can become pregnant (see "Contraception counseling"). ^[5]
• Pharmacological treatment
  • Estrogen therapy: Stop before surgery. ^[5]
  • Antihyperglycemics: Ensure optimized glycemic control.
  • See also "Preoperative medication management."

Choice of procedure is based on patient factors and the facility's experience. The most commonly performed procedures are described here. ^[5][6]

Sleeve gastrectomy

• Most common (approx. 60% of procedures) ^[7]
• Involves removal of ∼ 80% of the stomach, leaving a narrow tube-shaped portion ("sleeve") ^[8]
• Performed laparoscopically

Roux-en-Y gastric bypass

• Second most common (approx. 25% of procedures) ^[7]
• A small gastric pouch is created and the jejunum is attached to this pouch, bypassing the stomach and the upper small intestine. ^[6]
• Performed laparoscopically
• Results in greater weight loss than sleeve gastrectomy in the initial postsurgical years ^[9]

Metabolic and bariatric surgery typically results in approx. 20–30% reduction in total body weight through a combination of food-intake restriction, malabsorption, and neurohormonal changes. ^[6][10]

See "Postoperative management" for general guidance on the postoperative period.

Lifestyle modifications ^[5]

Lifestyle modifications aim to optimize nutrition and reduce the risk of complications (e.g., abdominal pain, dumping syndrome).

• Dietitian input
• Counsel the patient on:
  • Frequent, low-volume, high-protein meals
  • Eating slowly and stopping eating when full
  • Avoidance (or reduce intake) of simple carbohydrates and alcohol
  • Avoidance of smoking
  • Family planning: avoidance of pregnancy for 12–18 months after the procedure in individuals who can become pregnant ^[10]

Pharmacological therapy ^[5]

Micronutrient supplementation

The following are indicated in all patients following sleeve gastrectomy or Roux-en-Y gastric bypass:

• Chewable daily bariatric multivitamin with minerals containing the following amounts of necessary micronutrients ^[5]
  • Vitamin B1: 12 mg
  • Vitamin B12: 350–1,000 mcg
  • Folic acid: 800 mcg
  • Iron: 45–60 mg
  • Vitamin D3: 3000 IU
  • Vitamin A: 5000-10,000 IU
  • Vitamin E: 15 mg
  • Vitamin K: 90–120 mcg
  • Zinc: 8–22 mg
  • Copper: 1–2 mg
• Oral calcium citrate taken at least 2 hours apart from iron supplements or bariatric multivitamins ^[5]

Treatment of micronutrient deficiencies ^[5]

• Vitamin D deficiency: oral cholecalciferol OR ergocalciferol ^[5]
• Vitamin A deficiency
  • No corneal damage present: oral vitamin A ^[5]
  • Corneal damage present: intramuscular vitamin A ^[5]
  • Evaluate for concurrent copper and/or iron deficiencies.
• Folate deficiency: oral folic acid ^[5]
• Iron deficiency: oral ferrous gluconate with vitamin C supplementation for increased absorption ^[5][11]
• Vitamin B₁ deficiency ^[5]
  • Mild deficiency: IV vitamin B₁ ^[5]
  • Severe thiamine deficiency: IV vitamin B₁ ^[5]
  • Recurrent or refractory thiamine deficiency: Consider treatment of SIBO.
  • Patients at risk for refeeding syndrome: Add magnesium, potassium, and phosphate (see "Electrolyte repletion").
  • After deficiency has been treated, continue oral vitamin B₁.
• Zinc deficiency: Follow local protocols. ^[5]
• Vitamin B₁₂ deficiency: See "Vitamin B₁₂ replacement."
• Copper deficiency
  • Mild to moderate deficiency: oral copper gluconate ^[5]
  • Severe deficiency: intravenous cupric chloride (off-label) ^[5]
• Vitamin E deficiency (rare): Follow local protocols. ^[5]
• Vitamin K deficiency (rare)
  • Acute malabsorption: parenteral phytonadione ^[5]
  • Chronic malabsorption: oral or subcutaneous phytonadione ^[5]

Malabsorption following metabolic and bariatric surgery can cause micronutrient deficiencies.

Other pharmacological therapy ^[5][10]

Evaluate existing medications at each follow-up appointment, as absorption of some medications may change, and others may be reduced or discontinued if weight-related health conditions resolve.

• Ursodeoxycholic acid for 6 months postoperatively to reduce the risk of gallstones
• Diabetes medications for patients with T2DM
  • Adjust as needed to reduce risk of hypoglycemia.
  • Avoid medications that promote weight gain if possible (e.g., insulin, sulfonylureas).
  • Assess ongoing need for other diabetes medications (e.g., metformin).
• Adjust other medications as needed (e.g., antihypertensive agents, thyroxine).
• Avoid NSAIDs.

Avoid NSAIDs in patients who have had metabolic and bariatric surgery to reduce the risk of gastrointestinal ulcers. ^[5]

Follow-up ^[5][10]

Routine follow-up is performed at months 1, 3, 6, and 12 and then annually. Follow-up includes assessment of response to surgery and evaluation for complications.

Clinical evaluation

• Weight: A 20–30% reduction in total body weight is expected within 3 years of surgery. ^[6]
• Blood pressure
• Lifestyle (e.g., diet, exercise, community engagement)
• Clinical features of complications
  • Abdominal symptoms (e.g., pain, nausea, change in bowel habits)
  • Mental health symptoms (e.g., nonsuicidal self-injury, recreational substance use)

Diagnostic studies

• All patients
  • CBC, CMP
  • Vitamin B₁₂, folic acid, iron studies, vitamin D, vitamin A
  • Lipid panel, HbA1c
  • Additional testing for bone loss
    • Consider PTH, especially after Roux-en-Y gastric bypass.
    • Consider 24-hour urine calcium excretion ^[5]
    • DEXA scan: 2 years after surgery ^[5]
• Select patients
  • TSH: in patients with a known thyroid condition
  • Copper, zinc: after Roux-en-Y gastric bypass and as clinically indicated
  • Thiamine: in patients with risk factors for deficiency and as clinically indicated
  • Sleep study: in patients with obstructive sleep apnea after approx. 20% weight loss achieved ^[10]

Early complications ^[10][12]

• Bleeding
• Anastomotic leak
• Bowel obstruction
• Wound infection or dehiscence
• Venous thromboembolism
• Internal hernia
• See also "Postoperative complications."

Consider nongastrointestinal etiologies (e.g., acute coronary syndrome) for postoperative abdominal pain; patients undergoing metabolic and bariatric surgery may have additional comorbidities (e.g., coronary artery disease). ^[13]

Management ^[14]

Management is based on the clinical picture and may include the following.

• ABCDE survey
• Make NPO.
• Emergency preoperative evaluation (e.g., CBC, CMP, type and screen, crossmatch)
• Surgical consult
• Imaging
  • CT abdomen and pelvis with IV and oral contrast (preferred)
  • CXR and abdominal x-ray
• Further measures based on the underlying condition (e.g., broad-spectrum antibiotics if a leak is suspected)

Do not attempt nasogastric tube insertion without consulting the surgical team; altered anatomy increases the risk of injury from a blind insertion.

Late complications ^[10][12]

General

• Common
  • Nonspecific abdominal pain and/or nausea ^[10]
  • Malabsorption (e.g., protein-energy malnutrition, micronutrient deficiencies)
  • Early dumping syndrome, late dumping syndrome ^[10]
  • GERD and gastric ulcers
  • Effects of rapid weight loss (e.g., cold intolerance, fatigue, loose skin)
• Less common
  • Gallstones
  • Strictures
  • Internal hernia
  • Mental health complications (e.g., nonsuicidal self-injury, recreational substance use)
  • Loss of bone density
  • Calcium-oxalate kidney stones ^[10]
  • Bowel-associated dermatosis-arthritis syndrome

Roux-en-Y gastric bypass ^[10]

• Small intestinal bacterial overgrowth ^[10]
• Marginal ulcer ^[10]
• Gastrogastric fistula
• Bowel-associated dermatosis-arthritis syndrome
• Chronic diarrhea (e.g., from short bowel syndrome)

We list the most important complications. The selection is not exhaustive.